CN111451444A - Casting method of high-horsepower engine box body casting - Google Patents

Abstract

The invention discloses a casting method for a high-horsepower engine case casting, which includes preparing molding sand, molding and core making to obtain a sand mold; preparing a casting molten iron, and sending pig iron, returning material and scrap steel as raw materials into a smelting furnace for smelting; The smelted molten iron is inoculated and spheroidized in the bag, inoculated with flow before tapping, and then tapped; the molten iron is poured into the sand mold and inoculated with the flow, and the cold iron riser process is used for feeding and inoculation. Temperature control, casting is completed to form a casting; heat treatment is performed on the formed casting. The quality of the casting produced by the invention is good, and quality problems such as core sandwiching, shrinkage, cracks and the like are not easy to occur.

Description

A kind of casting method of high-horsepower engine case casting

technical field

The invention relates to the technical field of casting production of parts such as heavy-duty vehicles, large passenger cars, construction machinery and the like, in particular to a casting method for high-horsepower engine casing castings.

Background technique

In the "Catalogue of Major Technical Equipment and Products Supported by the State for Development" issued by the state, it is clearly pointed out that "high-power diesel engines and their key supporting equipment" are the direction of key support and priority development of the state. At present, high-power diesel engines are widely used in various fields of modern industry. They have a very wide range of applications and needs in my country's modern industry, and are also important and key equipment related to the development of my country's national economy.

In the high-power diesel engine and its key supporting equipment, the diesel chassis is the largest main component, and also the most important and critical component. Construction machinery, mining machinery, petroleum machinery, rail machinery, port machinery, electric locomotives, ship power, etc.

For automobile engines, the engine case is an indispensable part. At present, high-horsepower engine casings are mainly produced by casting. The most widely used casting method is the wet clay sand manufacturing process, which has the advantages of good forming performance, low energy consumption, low noise, less pollution, high efficiency and reliable operation. For the casting of multi-cavity high-horsepower engine cases, the inner cavity structure is complex and a large number of cores need to be used, resulting in core positioning, sand inclusion, core sandwiching, core sticking and core sticking during the casting process of high-horsepower engine cases. Bone and other problems are prominent, and at the same time, problems such as shrinkage, shrinkage, porosity, etc. will also have a serious impact on the quality of castings, which will eventually lead to low casting qualification rates and poor casting performance, and the difficulty of post-processing increases, and the processing quality is difficult to effectively guarantee. . In addition, the castings must be strongly ground with an oxygen melting rod or an air shovel in the subsequent treatment process, which not only easily leads to a secondary decrease in the quality and performance of the castings, but also increases the consumption of manpower and material resources and increases the production cost.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a casting method for high-horsepower engine casing castings, the quality of the obtained castings is good, and quality problems such as core sandwiching, shrinkage, cracks and the like are not easy to occur.

In order to solve the above-mentioned technical problems, the technical scheme adopted in the present invention is: a casting method for a high-horsepower engine casing casting, comprising the following steps:

a. Preparation of molding sand, molding and core making to obtain a sand mold;

b. Prepare molten iron for pouring, and send pig iron, return material and scrap steel as raw materials into the smelting furnace for smelting;

c. Carry out in-bag inoculation and spheroidization treatment on the molten iron, carry out flow inoculation before tapping, and then tap;

d. The molten iron is poured into the sand mold and inoculated with the flow, and the cold iron riser technology is used for feeding and temperature control, and the casting is completed to form a casting;

e. Heat treatment of the formed castings.

Further, the chemical composition of the molten iron includes: C 3.65-3.75wt%, Si2.25-2.45wt%, Mn 0.25-0.30wt%, S<0.02wt%, P≤0.045wt% , Cu 0.33-0.37wt%, Mg 0.03-0.05wt%, Ti≤0.045wt%; the rest are iron.

Further: in step a, the sand mold includes a casting cavity, a gating system, an overflow system and a riser system; the gating system is provided with a sprue, a runner, a filter screen and a plurality of inner runners; The bottom of the casting cavity is flush, a plurality of inner runners are symmetrically arranged on the bottom side of the casting cavity and communicate with the sprue, the runner and the sprue are connected, and the filter screen is arranged between the runner and the sprue; The overflow system includes an overflow inner runner, an overflow slag collecting bag and an overflow sheet arranged on the top of the sand mold; the riser system includes a heat preservation riser arranged on the top of the sand mold; the top of the sand mold is also provided with a plurality of There are several cold irons at the bottom of the sand mold.

Further: the cross-sectional area of the sprue is Σ _straight , the cross-sectional area of the runner is Σ _horizontal , the cross-sectional area of the inner runner is Σ _inside , the sum of the cross-sectional areas of the filter screen is Σ _cross , Σ _straight : Σ _horizontal . : _Within Σ: Σ _over = 1.8 to 1.9: 1.2 to 1.4: 1: 7.5.

Further: in step b, the proportion of raw materials is calculated as: 20-40% of pig iron, 40-60% of returned charge, and 20% of scrap steel by weight percentage.

Further, the compound inoculation method is adopted for the inoculation treatment, and the compound spheroidization method is adopted for the spheroidization treatment.

Further: compound the 6RE nodulizer nodulizer with a particle size of 5 to 25mm and a weight of 0.8wt% of the molten iron and a QRMg6RE2 nodulizer with a weight of 0.4wt% of the molten iron, and put it into a dam type nodulizer. The bottom layer is tamped; the second layer is covered with 75 ferrosilicon with a particle size of 3 to 12 mm and a weight of 0.1 wt % of the molten iron and tamped; the third layer is completely covered with a weight of 0.6 to 0.8 wt % of the molten iron. Shred steel and compact; cover gaps with slag remover.

Further: in step c, a silicon-barium inoculant with a particle size of 3-12 mm and a weight of 0.5 wt % of the molten iron is poured into the molten iron ladle at one time to inoculate with the tap.

Further: in step d, when the molten iron is poured, a Bi inoculant with a particle size of 0.2-0.8 mm and a weight of 0.13 wt% of the molten iron is added along with the flow; the molten iron casting temperature is 1350±10°C.

Further: in step e, the temperature of the furnace during heat treatment is controlled below 200°C, the heating rate is ≤35°C/h, and the temperature is maintained at 560-580°C, and the holding time is 4-8h; ≤25℃/h, cool to the release temperature <200℃ and then air-cool to room temperature.

The beneficial effects of the present invention are:

1. By controlling the composition of the molten iron and making full use of the significant graphitization expansion effect of the spherical graphite in the molten iron, self-feeding during the casting molding process is realized, which effectively reduces defects such as shrinkage porosity and shrinkage cavities, and improves the casting quality. quality and yield;

2. Using compound spheroidizing treatment, different elements in different spheroidizing agents have different effects and effects on the spheroidizing process, and the rare earth contained in the 6RE nodulizer spheroidizing agent is used to ensure the stability of the spheroidizing effect. The Mg element contained in the QRMg6RE2 spheroidizing agent improves the spheroidizing effect of graphite in the molten iron, and the spheroidizing stability and spheroidizing effect are greatly improved;

3. The compound inoculation treatment is adopted to ensure the full inoculation of the molten iron through multiple uninterrupted inoculations, which can not only hinder the growth of the matrix grains, but also effectively increase the number of graphite and refine the graphite, thereby improving the spheroidization level and forming a stable The nucleation particles provide good conditions for the spheroidization reaction;

4. The pouring system of molding sand adopts double-side bottom pouring pouring and overflow system compound pouring, which effectively ensures good filling speed and filling pressure of molten iron, improves the filling degree of castings, and makes the filling process stable. Reduce the scouring force on the cavity;

5. The cold iron riser technology is adopted, and the air outlet sheet, the heat preservation riser set at the top of the sand mold and the cold iron set at the bottom of the sand mold are used to perform good feeding and cooling temperature control of the whole box casting, so as to ensure the intake and exhaust of the gating system. unobstructed.

Description of drawings

Fig. 1 is the casting cavity schematic diagram of sand mould in the present invention;

Fig. 2 is the top schematic diagram of sand mould in the present invention;

Fig. 3 is the bottom schematic diagram of sand mould in the present invention;

Fig. 4 is the process diagram of heat treatment in the present invention;

Marked as: 100-casting cavity, 210-sprue, 220-runner, 230-filter, 240-inner runner, 310-overflow inner runner, 320-overflow slag bag, 410 -Insulation riser, 510-gas outlet, 520-cold iron.

Detailed ways

In order to facilitate understanding of the present invention, the present invention will be further described below with reference to the accompanying drawings and embodiments.

The casting method of a high-horsepower engine casing casting according to the present invention comprises the following steps:

Step 1: Preparing molding sand, resin flow rate/sand flow rate is 0.75-1.15wt% in molding sand preparation process, curing agent flow rate/resin flow rate are adjusted according to different seasons, 35-50wt% in winter, 25-40wt% in summer ; After the molding sand preparation is completed, modeling and core making are performed. Due to the complex shape of the high-horsepower engine casing casting, many cores are used in the molding process, and the positioning of the core is the most important link in the entire molding process. The accuracy of the casting is directly related to the dimensional accuracy of the inner cavity of the casting. If there is a deviation in the positioning of the core, the dimensional accuracy of the casting will not meet the requirements for use, and eventually the product will be scrapped. In the present invention, in order to ensure the precise positioning of many cores , Before assembling the core, set the axis positioning rod at the main position of the cavity, along the axis positioning rod to position and assemble the discrete cores in sequence, so as to ensure the accurate positioning of the core, which can effectively improve the high-horsepower engine case. The dimensional accuracy of the inner cavity of the body casting.

The sand mold structure prepared by the present invention is shown in Figures 1 to 3. The sand mold includes a casting cavity 100, a pouring system, an overflow system and a riser system; the pouring system is provided with a sprue 210, a runner 220, a filter 230 and a plurality of inner runners 240; the runner 220 is flush with the bottom of the casting cavity 100, and the multiple inner runners 240 are symmetrically arranged on the bottom side of the casting cavity 100 and communicate with the runner 220. The sprue 210 is connected, and the filter screen 230 is arranged between the sprue 220 and the sprue 210. The present invention adopts a bottom-casting double-side pouring system, and uses a three-sided surrounding inner sprue 240 to supply molten iron to the bottom of the casting ; The overflow system includes an overflow inner runner 310, an overflow slag collecting bag 320 and an overflow sheet arranged on the top of the sand mold; the riser system includes a thermal insulation riser 410 arranged on the top of the sand mould, and the thermal insulation riser 410 is arranged in the molten iron. The temperature is lower; the top of the sand mold is also provided with a plurality of air outlet sheets 510, and the bottom of the sand mold is provided with a plurality of cold irons 520. The cold iron 520 includes a traveling cold iron and a qualitative cold iron, which are respectively arranged in the casting process of the high-horsepower engine box. The location of each thermal node in . During pouring, the molten iron enters the sand mold from the sprue 210, then passes through the filter screen 230 and is dispersed into the runners 220 left and right, and enters each inner runner 240 along the strip-shaped runners 220. The casting cavity 100 is gradually filled from the bottom to the bottom, and the air is discharged at the same time. The pouring is completed quickly, the filling pressure is stable and the exhaust is smooth during the pouring process, which ensures the quality of the castings.

Considering that the molten iron will scour the cavity during the pouring process, in the present invention, the cross-sectional areas of the sprue 210, the runner 220, the filter screen 230 and the inner runner 240 are limited, and the cross-sectional area of the sprue is set to be The cross-sectional area of Σ _straight and the runner is Σ _horizontal , the cross-sectional area of the inner runner is Σ _inside , and the sum of the cross-sectional areas of the filter is Σ _over , to ensure that the ratio of Σ _straight : Σ _horizontal : Σ _inside : Σ _over is in the range of 1.8～1.9:1.2～1.4:1:7.5, keep the micro-pressure flow state when the molten iron fills the pouring system, the scouring force to the cavity is small, and it has a good slag blocking ability, which can ensure the stable filling and filling. Time is reasonable. In addition, in order to obtain good venting effect and feeding effect, it is ensured that the total cross-sectional area of the venting holes on the venting sheet 510 is greater than or equal to the sum of the cross-sectional areas of the multiple inner runners 240 .

After the sand mold is prepared, the casting paint is painted on the sand mold. The foundry paint can dry the sand mold during the combustion process and reduce the water content of the sand, so as to solve the problem of poor air permeability and high water content in the sand when casting large-scale high-horsepower engine box castings. resulting in casting defects. In the present invention, Foseco 800 casting coating is used, which has good suspension stability, excellent thixotropy and leveling, no brush marks after painting, firm coating, low gas generation, easy ignition, high combustion value, and anti-sticking properties. Good sandiness, smooth casting surface. In the foundry coating, 0.2-0.5% of the weight of the foundry coating can be added with hemp fiber to further increase the air permeability.

Step 2: Prepare molten iron for pouring, and send pig iron, returning material and scrap steel as raw materials into a smelting furnace for smelting; the ratio of raw materials is calculated by weight percentage as follows: pig iron 20-40%, returning material 40-60%, scrap steel 20% The chemical composition of the molten iron obtained after smelting includes: C 3.65-3.75wt%, Si 2.25-2.45wt%, Mn 0.25-0.30wt%, S<0.02wt%, P≤0.045wt%, Cu 0.33 ～0.37wt%, Mg 0.03～0.05wt%, Ti≤0.045wt%, and the rest are iron; using the molten iron of the above components, the significant graphitization expansion effect of spherical graphite in the molten iron is used to realize the self-condensation during the casting forming process. Feeding can effectively reduce defects such as shrinkage porosity and shrinkage cavity, and improve the quality and yield of castings.

Step 3, compound the 6RE nodulizer nodulizer with a particle size of 5 to 25 mm and a weight of 0.8wt% of the molten iron and a QRMg6RE2 nodulizer with a weight of 0.4wt% of the molten iron, and put it into the most important part of the dam-type nodulizer bag. The bottom layer is tamped, the second layer is covered with 75 ferrosilicon with a particle size of 3 to 12 mm and a weight of 0.1 wt % of the molten iron and tamped, and the third layer is completely covered with 0.6 to 0.8 wt % of the molten iron. The steel sheet is compacted, and the slag remover is covered at the gap; through the compound spheroidizing treatment method, the rare earth contained in the 6RE nodulizer spheroidizer is used to ensure the stability of the spheroidization, and the Mg contained in the QRMg6RE2 spheroidizer is used to ensure the stability of the spheroidization. Elements improve the spheroidization of graphite in molten iron; use 75 ferrosilicon to inoculate in the ladle, and then inoculate the silicon-barium inoculant with a particle size of 3 to 12 mm and a weight of 0.5wt% of the molten iron into the iron at one time. In the liquid sack, the tap-to-flow inoculation is carried out.

Step 4, pour the molten iron into the sand mold, and the pouring temperature of the molten iron is 1350±10°C; when pouring the molten iron, add a Bi inoculant with a particle size of 0.2-0.8 mm and a weight of 0.13wt% of the molten iron; In the process, the cold iron riser technology is used for feeding and temperature control, and the whole box casting is well fed and cooled by the air outlet 510, the heat preservation riser 410 and the cold iron 520 arranged at the bottom of the sand mold. Temperature control ensures smooth intake and exhaust of the gating system; casting is completed to form castings.

The composite inoculation treatment method adopted in the above-mentioned steps of the present invention is inoculation in the bag, inoculation by tapping and inoculation with pouring, and the sufficient inoculation of the molten iron is ensured through multiple uninterrupted inoculation; the Bi element contained in the Bi inoculant can both It can hinder the growth of matrix grains, and can effectively increase the number of graphite and refine the graphite, thereby improving the spheroidization grade, forming stable nucleation particles, and providing good conditions for the spheroidization reaction; the silicon and barium elements in the inoculant have good The addition of silicon and barium elements is only half of the addition of 75 ferrosilicon inoculant in the traditional inoculation method, which ensures the inoculation effect and reduces the inoculation cost.

Step 5. Heat treatment of the formed casting. The specific process of heat treatment is shown in Figure 4. The temperature of the furnace is controlled below 200 °C, the heating rate is ≤ 35 °C/h, and the temperature is maintained at 560 to 580 °C. The holding time is 4 ~8h; cool down after the heat preservation, the cooling rate is ≤25℃/h, cool down to the release temperature <200℃, and then air-cool to room temperature.

Example 1

Using EN-GJS-500-7 ductile iron, the chemical composition of the molten iron obtained by smelting includes: C3.66%, Si 2.27%, Mn 0.26%, P 0.023%, S 0.10%, Cu 0.34%, Mg 0.03%, Ti 0.026%, and the balance is Fe. According to the above steps of the present invention, a high-horsepower engine case casting is prepared. After cooling, the tensile strength Rm of the casting is tested by the SHT4305 microcomputer-controlled electro-hydraulic servo universal testing machine. -3000 Brinell hardness tester tests the hardness HBS of the casting, and the measured Rm is 535MPa and the HBS is 186.

Example 2

Using EN-GJS-500-7 ductile iron, the chemical composition of the molten iron obtained by smelting includes: C3.70%, Si 2.30%, Mn 0.27%, P 0.022%, S 0.09%, Cu 0.35%, Mg 0.04%, Ti 0.029%, and the balance is Fe. According to the above steps of the present invention, a high-horsepower engine case casting is prepared. After cooling, the tensile strength Rm of the casting is tested by the SHT4305 microcomputer-controlled electro-hydraulic servo universal testing machine. -3000 Brinell hardness tester tests the hardness HBS of the casting, and the measured Rm is 543MPa and the HBS is 203.

Example 3

Using EN-GJS-500-7 ductile iron, the chemical composition of the molten iron obtained by smelting includes: C3.71%, Si 2.40%, Mn 0.28%, P 0.020%, S 0.08%, Cu 0.36%, Mg 0.03%, Ti 0.035%, and the balance is Fe. According to the above steps of the present invention, a high-horsepower engine case casting is prepared. After cooling, the tensile strength Rm of the casting is tested by the SHT4305 microcomputer-controlled electro-hydraulic servo universal testing machine. -3000 Brinell hardness tester tests the hardness HBS of the casting, and the measured Rm is 551MPa and the HBS is 213.

Compared with the standard parameters of mechanical properties of high-horsepower engine case castings, Rm≥500MPa and HBS of 170-230, the mechanical properties of the above three embodiments of the present invention fully meet the index requirements of high-horsepower engine cases, and the production qualification rate of the castings up to 95%.

Claims (10)

1. a casting method of high-horsepower engine casing casting, is characterized in that: comprise the following steps: a. Prepare molding sand, obtain sand mold after molding and core making, and apply casting paint on the sand mold; b. Prepare molten iron for pouring, and send pig iron, return material and scrap steel as raw materials into the smelting furnace for smelting; c. Carry out in-bag inoculation and spheroidization treatment on the molten iron, carry out flow inoculation before tapping, and then tap; d. The molten iron is poured into the sand mold and inoculated with the flow, and the cold iron riser technology is used for feeding and temperature control, and the casting is completed to form a casting; e. Heat treatment of the formed castings. 2 . The method for casting a high-horsepower engine case casting according to claim 1 , wherein the chemical composition of the molten iron comprises: C 3.65-3.75wt%, Si 2.25-2.45wt%, Mn 0.25 ～0.30wt%, S<0.02wt%, P≤0.045wt%, Cu 0.33～0.37wt%, Mg 0.03～0.05wt%, Ti≤0.045wt%; the rest are iron. 3. The casting method of a high-horsepower engine case casting as claimed in claim 1, wherein in step a, the sand mold comprises a casting cavity, a gating system, an overflow system and a riser system; the gating system is provided with The sprue, the runner, the filter screen and the multiple inner runners; the runner is flush with the bottom of the casting cavity, and the multiple inner runners are symmetrically arranged on the bottom side of the casting cavity and communicate with the runner. The runner is communicated with the sprue, and the filter screen is arranged between the runner and the sprue; the overflow system includes an overflow inner runner, an overflow slag collecting bag and an overflow sheet arranged on the top of the sand mold; The riser system includes a heat preservation riser arranged on the top of the sand mold; the top of the sand mold is also provided with a plurality of air outlet sheets, and the bottom of the sand mold is provided with a plurality of cold irons. 4. The casting method of a high-horsepower engine case casting as claimed in claim 3, wherein the cross-sectional area of the sprue is Σ _straight , the cross-sectional area of the runner is Σ _horizontal , and the cross-sectional area of the inner runner is Σ horizontal. The area is _within Σ, the sum of the cross-sectional areas of the filter screen is Σ _over , Σ _straight : Σ _horizontal : Σ _inside : Σ _over = 1.8～1.9:1.2～1.4:1:7.5. 5. The casting method of a high-horsepower engine casing casting as claimed in claim 1, characterized in that: in step b, the proportion of raw materials by weight is: pig iron 20-40%, return charge 40-60% , Scrap 20%. 6 . The casting method of a high-horsepower engine case casting as claimed in claim 1 , wherein the compound inoculation method is adopted for the inoculation treatment, and the compound spheroidization method is adopted for the spheroidization treatment. 7 . 7. the casting method of a kind of high-horsepower engine casing casting as claimed in claim 6 is characterized in that: the 6RE nodulizer nodulizer and the weight that the granularity is 5～25mm, the weight is the molten iron weight 0.8wt% and the iron The QRMg6RE2 nodularizing agent with a liquid weight of 0.4wt% is compounded, put into the bottom layer of the dam-type nodularizing bag and tamped; the second layer is covered with 75 ferrosilicon with a particle size of 3-12mm and a weight of 0.1wt% of the molten iron. and tamping; the third layer is completely covered with 0.6-0.8 wt % of the molten iron weight of broken steel pieces and compacted; the gap is covered with a slag remover. 8. The casting method of a high-horsepower engine casing casting as claimed in claim 6, wherein in step c, the silicon-barium inoculant whose particle size is 3～12mm and whose weight is 0.5wt% of molten iron is used once Sexually rush into the molten iron ladle to carry out the inoculation of the iron with the flow. 9. The casting method of a high-horsepower engine case casting as claimed in claim 6, wherein in step d, when pouring molten iron, the granularity added with the flow is 0.2～0.8mm, and the weight is the molten iron weight 0.13wt % Bi inoculant; molten iron casting temperature is 1350±10℃. 10. The casting method of a high-horsepower engine case casting as claimed in claim 1, characterized in that: in step e, the temperature of the furnace during heat treatment is controlled to be below 200°C, the heating rate is ≤35°C/h, and the temperature reaches 560 to 560°C. Heat preservation after 580℃, and the holding time is 4-8h; after the heat preservation, cool down, the cooling rate is ≤25℃/h, cool down to the release temperature < 200℃, and then air-cool to room temperature.

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